1. Field of Endeavor
The present invention relates to shape memory systems and more particularly to shape memory polymers.
2. State of Technology
U.S. Pat. No. 3,624,045 (Stivers) describes the development of crosslinked polyurethanes exhibiting such properties.
U.S. Pat. No. 5,049,591 (Hayashi)—The use of the term “shape memory polymer” appears to start with U.S. Pat. No. 5,049,591 (Hayashi), who describes compositions of polyurethanes which could be suitable for thermally insulating foams which utilize the shape memory effect for application and transportation advantages.
U.S. Pat. No. 5,330,483 (Heaven) appears the first to use shape memory polymers in a medical application, using them in a fiber mesh comprising a tissue isolation bag. They are used for the shape recovery property of an SMA or SMP mesh to pulverize tissue in the bag.
U.S. Pat. No. 5,603,772 (Phan) describes the use of SMPs in intravascular stents. This patent provides example geometries for a stent and provides examples of SMP materials. This patent also describes an endoprosthetic device with therapeutic compound (U.S. Pat. No. 5,674,242).
U.S. Pat. No. 5,762,630 (Bley) described an SMP thermally softening catheter stylet. This allows the catheter to be stiff (below Tg) external to the vasculature and soft (>Tg) within the vasculature.
U.S. Pat. No. 5,911,737 (Lee) and U.S. Pat. No. 6,059,815 (Lee) describes the use of SMPs for micro-actuators used to controllably release arbitrary objects within vascular passageways. These patents describe heating methods to achieve actuation including optical heating, resistive heating, and convective heating using a heat transfer fluid. U.S. Pat. No. 6,086,599 (Lee) also describes SMP micro-structures used to form mated connections which can be used to reposition or remove devices from otherwise inaccessible places within the body such as the vasculature.
U.S. Pat. No. 5,957,966 (Schroeppel) describes an implantable tubular sleeve used as a catheter, cardiac stimulator lead, or shunt made out of SMP. The lead can be positioned within a vascular passageway while compliant and allowed to harden, taking on the shape of the vessel.
U.S. Pat. No. 5,964,744 (Balbierz) describes the use of SMPs in devices for swellable ureteral stents. The SMP acts to hold a second material in a collapsed state. Upon actuation, which occurs when the SMP swells at the site of use, the whole structure is able to expand. A large number of specific polymer systems are described.
U.S. Pat. No. 6,090,072 (Kratoska) describes an SMP expandable introducer sheath, utilizing the shape memory effect to allow it to expand in diameter after intruction through a relatively small puncture. The sheath can then be expanded to the needed size during the procedure with no further trauma to point to insertion.
U.S. Pat. No. 6,102,917 (Maitland) and International Patent No. WO0003643 (Maitland) describe an SMP micro-gripper which is optically actuated, and can be used to release devices such as embolic coils at targeted sites within the body. The occurrence of actuation can be detected via the same optical system used for actuation.
U.S. Pat. No. 6,388,043 (Langer) describes SMP compositions, articles of manufacture, methods of preparation and use. Compositions allow for polymer segments to be linked via functional groups which may be cleaved in response to application of energy. U.S. Pat. No. 6,160,084 (Langer) describes biodegradable shape memory polymer compositions, methods of manufacture and preparation, and use.
WO 95/26762, published Oct. 12, 1995, Bruin, et al discloses thermal shape memory biodegradable polymers that are useful for manufacture of stents. The SMP include amorphous non-crystallizable polylactic acid networks, the highly cross-linked networks, that also include the conversion products of star prepolyesters such as those based on lactic acid copolymers with diisocyanate.